This invention relates to a process for applying nickel on a refractory metal surface. More particularly, it relates to an improved and simplified electroplating process used to obtain an adherent nickel layer on a refractory metal surface.
Refractory metals are used for many purposes, such as rocket nozzles and other "hot structures" capable of supporting aerodynamic and thermal stresses, as well as for insulation-backed heat shields protecting low-temperature structural members. However, because the surfaces of these refractory metals are susceptible to corrosion and frictional wear, it is often necessary or recommended to plate them with other metals, such as chromium, copper and nickel. Unfortunately, refractory metals such as titanium and tantalum are often difficult to plate satisfactorily with an adherent metal coating. For instance, when attempts have been made to apply a metal coating, such as nickel or chromium, on tantalum, the tantalum spontaneously undergoes oxidation to form an oxide film on its surface, and the oxide surface interferes with the chemical bonding of a subsequently deposited nickel layer.
Refractory metals are more readily coated with nickel by electroplating means, as opposed to electroless plating means. However, the electroplating methods often involve a two-step deposition procedure in which a heat treatment to induce diffusion bonding is required between the steps. For instance, in Electrodeposition of Nickel or Tantalum by A. Yaniv (Transactions of the Institute of Metal Finishing, 1970, Vol. 48, pp 5-10), an adherent nickel deposit is applied on tantalum by plating in two stages, with a heat treatment between the stages. The intervening heat treatment generally requires preliminary rinsing and drying steps, and the heat-treated deposit must be reactivated prior to resumption of plating. This complicates the entire plating process, thereby resulting in increased processing and handling time requirements which, in turn, result in high production costs.
It is an object of this invention to provide an improved process for plating nickel on a refractory metal surface which is not subject to the above-mentioned problems and disadvantages.
It is another object of this invention to provide an improved process for plating nickel on a refractory metal surface.
It is a further object of this invention to simplify the process for electroplating nickel on a refractory metal surface while insuring the adherence of nickel to the surface.
Other objects and advantages of the invention will become apparent as the description thereof proceeds.